Work locating apparatus

ABSTRACT

A work locating apparatus having a tension member actuated by an actuating member, particularly an actuating piston, via a starting stroke and a working stroke in which a pneumatic cylinder constitutes a control means and a mechanical step-up mechanism is operable between the control means and the tension member with the actuating member abutting directly the tension member by the starting stroke and the step-up mechanism by the working stroke of the tension member.

I United States Patent 1191 Weiss May 28, 1974 1 WORK LOCATING APPARATUS[76] Inventor: Dieter Weiss, Wilhelmstrasse 58, m Examufer EdgarGeoghegm.

Neckarweihingen Germany Assistant Examiner-Abraham Hershkovitz Attorney,Agent, or Firm-Holman & Stern [22] Filed: Apr. 28, 1972 21 Appl. No.2248,455 57 ABSTRACT A work locating apparatus having a tension member[52] US. Cl 92/14, 92/25, 92/29, actuat d by an actuating member,particularly an ac- 92/65 tuating piston, via a starting stroke and aworking [51] hit. C1. F151) 15/22 troke in which a pneumatic cylinderconstitutes a Fleld of Search 65 control means and a mechanical step-upmechanism is v operable between the control means and the tensionReferences Cited member with the actuating member abutting directlyUNITED STATES PATENTS the tension member by the starting stroke and the1,965,106 7 1934 McDougall 92/29 x p-"P mechanism y the Working Strokeof the 3,135,171 6/1964 Michalak, J1 92/29 X member- 13,160,078 12/1964Hiemstra et a1... 92/14 3,320,861 5/1967 Johnson et al 92 14 22 (718M516D'awmg Flgures 35 i g 40 I WORK LOCATING APPARATUS BACKGROUND OF THEINVENTION The present invention relates to a work locating apparatushaving a tension member which is actuated by means of an activatingdevice, especially an actuating piston via a starting stroke and aworking stroke, which actuating means is formed especially by apneumatic cylinder, and the direction of the actuating means beingmovably adjustable.

PRIOR ART in which the actuating member actuates the tension member bymeans of the starting stroke directly, and actuates a mechanical step-upmechanism by means of the working stroke of the tension member, with thestep-up mechanism functioning between a control means and the tensionmember. During the starting stroke, the tension device is unstressed andthe tension member may now be moved by means of the starting strokewithout the need for a substantial use of forces. Due to the fact thatthe comparatively short working stroke, which requires a large force, iseffected via a mechanical step-up mechanism, abd because the stepupmechanism is supported against the cylinder, with the power course beingthus made to the tension member via the cylinder and step-up mechanism,while the actuating piston of the pneumatic cylinder-piston unitactuates the step-up mechanism, a substantial power saving is obtained.If there is a need for utilizing the entire tension strength of thepiston of the unit, there is then a need for subjecting the cylinder toa high pressure, while such a pressure is unavailable in most of theworkshops. As the step-up mechanism is not supported against the pistonbut rather immediately against the .cylinder, and the piston effectsonly the actuation of the step-up mechanism, very large tensional forcescan be provided with a low pressure in the cylinder.

SUMMARY OF THE INVENTION According to the instant invention, thearrangement is preferably such that the step-up mechanism is providedwith a sensor or feeler which is mounted suitably on the inside wall ofthe cylinder which forms the control, with the feeler disconnecting theactuating member from the tension member independently of the design ofthe control at the end of the working stroke, and moving the step-upmechanism into the working position. The step-up mechanism is switchedon and started by means of the feeler according to a pre-set course,i.e. at the end of the starting stroke. It is advantageous that thestep-up mechanism be constructed to be selflocking. Since the pressurein the cylinder during the working stroke serves only for the actuationof the stepup mechanism, the tension force of the device may be retainedalso when the working area of the actuating cylinder becomesdepressurized.

According to a preferred embodiment of the instant invention, thestep-up mechanism is provided with a power-transmission member which issupported on a support area in the working position at the control andat the tension member, that is, on one of these parts, whereby thesupport area is positioned at a right angle to the stroke-direction.This power transmission member now functions similarly to a wedgebetween the cylinder and the tension member which, in this way, is thusmoved forward with great force. The arrangement is effected in such away that the tension member is in a disconnectable connection with thestarting member, with a swingable lever being pivotally arranged on thetension member, and constituting simultaneously the sensor and the powertransmission members, and the starting member being provided with awedge area which is inwardly inclined in a direction opposite to thestroke direction, whereby the wedge-area, during the working stroke,presses the power transmission member against the support area of thecontrol which is positioned transversely to the stroke direction.

In a preferred embodiment of the instant invention, the starting memberconsists of an annular piston which encircles a central piston connectedwith the tension member, and the annular piston has a collet or sleevewhich encircles the central piston, with the collet being provided withthe wedge-area. The central piston is formed with a clearance into whichis secured a control section of the lever, located at a distance fromthe rocking axis, with the control section being secured by that part ofthe lever which abuts or engages the cylinder wall and which constitutesthe sensor or feeler, with the front edge of the collet engaging thecontrol section during the starting stroke, and the cylinder beingprovided with a recessed area, which is delineated axially on that sidewhich is closest to the actuating piston by means of the support areapositioned transversely to the stroke-direction, and in which that partof the lever constituting the sensor, drops at the end of the actuatingstroke, whereby the control section of the lever is moved to theinclined area of the collet. It is advantageous that the recessed areaof the cylinder be constructed as a circular area and the clearance ofthe central piston be defined by an annular groove, with a plurality ofswinging levers being evenly positioned about the circumference of thecentral piston on the tension member. Thus, the levers, together withthe tension member, are moved by means of the annular piston over thecollet, during the starting stroke, whereby the levers, by their restingonto the front edge of the collet, carry with them the tension member.After completion of the starting stroke, the part of the lever whichconstitutes the sensor, can enter the circular area of the cylinder, sothat the level releases the central piston and the control section ofthe lever runs freely onto the wedgeor inclined area of the colletperiphery, whereby the lever, during the further stroke of the annularpiston, which constitutes the starter piston, is continuously forceddeeper into the annular groove of the central piston, and moves thetension member forward with great force. The central piston, which isadvantageously connected with the tension member, remains thereby inplace, since the tension member only completes a very small workingcourse. If the support area, against which the sensor of the lever ispressed or forced, is positioned vertically to the stroke direction,then a cpmparatively small working stroke is obtained through theswinging of the lever. The arrangement is, however, advantageous in thatthe support area is in forms the control means and inclined inwardlytowards the starting piston, and is preferably constructed as a conicalarea, whereby the working course is increased.

, tion during a pressure-decrease, it is then able to push the colletback over this section, and in such case, an

- inwardly inclined section is more advantageous to prevent the furtherdisplacing of the collet. For this case,

I it is necessary to provide for a pressure means, which transmits thetensional force, which is supported against the tension member underinterpolation of a spring, which is being compressed at the end of theworking stroke. In a case in which, during a pressure loss, the controlmeans of the lever is at that moment touching an outwardly inclinedsection of the collet and the starter piston moves together with thecollet until the control member reaches an inwardly inclined orcylindrical section, this stroke of the tension member is then acceptedby the spring without a substantial decrease of the tension strength.

Due to the self-locking construction of the mechanical step-upmechanism, the tension device also remains in the tension position aftera pressure release from the working area of the starting piston iseffected. It is therefore necessary that in this situation a specialarrangement be provided for releasing the tension member. This may beaccomplished in that the tension member is cylindrical in shape and isguided in a collar of the cylinder which forms the control, with thecircular area being provided with a pressure-connection means. Through apressurizing of the circular area, the

' starting piston is thereby engaged in the counter direction. Theannular piston is moved back and the collet releases the control memberof the levers, whereby the work locating apparatus is again moved backto its original position.

The instant invention thus enables the utilization of air-pressure pipesavailable in each workshop, which supplies only comparatively lowpressures, for using high tension forces.

BRIEF DESCRIPTION OF THE DRAWINGS The instant invention is schematicallyillustrated in the drawings by exemplary embodiments, in which FIGS. 1and 2 illustrate partly in elevation and partly in cross section oneembodiment of the work-locating device in the starting position and thetension position, respectively; FIG. 3 is a fragmentary view on anenlarged scale of the collet according to FIGS. l and 2 and FIGS. 4 and5; FIGS. 4 and 5 are views similar to FIGS. 1 and 2 of anotherembodiment of the work locatingapparatus in its starting position andthe tension position, respectively, and FIG. 6 illustrates an alteredembodiment partly in elevation and partly in cross section, of the worklocating device in its starting position.

DETAILED DESCRIPTION OF THE INVENTION In the embodiment according toFIGS. 1 to 3, a pneumatic cylinder 1 is closed by a bottom piece 2,fixedly attached to the cylinder 1. In the cylinder 1 is tightly guidedan annular piston 3 which constitutes an actuating piston of thepneumatic system, and a central piston 4 is tightly guided in theannular piston 3. A collar or flange 5 of the piston 4 coacts with theouter surface of the piston 3 to limit the movement of the piston 4opposite the piston 3. A pressure connecting means 6 is provided in thebottom piece 2 for supplying pressurized air to a working area or space7 for the piston 3 or piston 4. A collar 8 is located at the end of thecylinder 1 remote from the bottom piece 2, with the collar being formedby a circular part 9 fixedly connected with the cylinder. A circularspace 16 is formed in the part 9, and the part 9 is delimited at itsside facing the piston 3 by an area 17 of a flat conical shapepositioned transversely to the axis of the cylinder 1. Apressureconnecting means 23 is associated with the circular part 9 andcommunicates with the space 16.

A cylindrical tension part 10 is tightly positioned in the collar 8 anda portion thereof extends into the cylinder 1. The piston 4 has ashoulder 26 with which it is supported towards an inwardly extendingflange 27 of the part 10. A plurality of swinging levers 11 are mountedon axles 12 of the cylindrical part 10 and are evenly positioned aroundthe circumference of the central piston 4. The levers 11 are of a forkedshape and guide-rollers 14 are rotatably positioned on axles 15 providedbetween fork-arms 13 of the levers. The piston 4 is provided with anannular groove 18 in which the guide rollers 14 are located while thestarting stroke is at an idle position (FIG. 1). A nose 19 of the levers11, which constitutes a sensor or feeler abuts or engages inner wall 20of the cylinder 1, and holds the guide-rollers 14 in their position inthe annular groove 18. A collet orv sleeve 21 is fixedly connected tothe piston 3, encircling loosely the central piston 4, and a front areaor edge 22 thereby coacts with the guide rollers l4.

When the space 7 is placed under pressure via the pressure connection 6,the piston 3 and piston 4 move into the direction of the strokeindicated by arrow 24. The front edge 22 of the collet 21 thus pushesagainst the guide-rollers l4 and levers 11 try to swing outwardly aboutthe axles 12 into the stroke direction 24, but such a movement islimited since the noses 19 engage the wall 20 of the cylinder 1. As soonas the noses 19 enter the area of the recess 16, the noses move or dipso to speak into the recess 16. This is effected as the front edge 22 ofthe collet 21 engages eccentrically at the guide rollers 14, therebyresulting in a force component towards the outside. The levers 11,together with the guide rollers 14 and the noses l9, reach the positionsl1, l4, 19' in FIG. 2. The guide rollers 14 roll on the periphery of thecollet 21 and leave the annular groove 18 and hence the piston 4. Thestarter stroke ends in this position.

The collet 21 enters into an annular space 25 between the piston 4 andthe part 10, whereby the annular piston 3 continuously moves furtherinto the direction 24. The piston 4 moves into the direction 24 onlyuntil it meets resistance. Since the starting stroke is measured so thatat the end of such stroke the working stroke begins, the piston 4 willonly very slowly continue its stroke, when the levers 11 together withthe noses 19 enter the recess 16.

The mechanical step-up mechanism is defined by the collet 21, the levers11 together with the feelers l9 and the guide rollers 14. The furtherthe annular piston is lifted, the further movement of the collet 21 inthe annular space 25 and the further the guide rollers 14 and the levers11 are pushed outwardly, so that the guide rollers 14 now function aspressure measn which support themselves on the area of flat conicalshape 17. The tension part is thereby displaced with great force by asmall distance into the direction 24, as shown in FIG. 2.

The collet 21 is illustrated on a larger scale in FIG. 3. At the freeend, adjacent the front edge 22, the periphery has an outwardly inclinedguide area or section 28 for the guide rollers 14, which, merges with acylindrical guide area 29. The guide area 29 merges with a furtheroutwardly inclined guide area 30, while an inwardly inclined guide area31 merges with the guide area 30. Instead of the cylindrical guide area29, there may be provided also a guide area which is inwardly inclinedand in place of the inwardly inclined guide guide area 31 there may be acylindrical guide area.

As long as the guide rollers 14 move on the outwardly inclined guideareas 28 and 30, the levers are pushed outwardly and this is inaccordance with the working the area 31. Due to this self-locking, theannular piston 3 remains in its position 3', in which the levers 11together with the feelers 19, are pressed into the circular area 16 andbecause of pressure relief in the working space 7, a resetting of thetension part 10, from the working area 10 cannot be effected. In orderto effect the resetting, the circular area 16 is pressurized via theconnecting means 23. The annular piston 3 is moved in a directionopposite to the stroke direction 24, the collet 21 which is in theposition 21' is drawn from the annular area 25, and the tension devicemoves back into the starting position, shown in FIG. 1.

As illustrated, a piston-shaped insertable member 32 is guided in thetension part 10 to be axially movable, and is biased by a spring 33towards the flange 27 of the tension member 10. The member 32 carries athreaded connection member 34 to which may be connected any type ofadapter piece for the purpose of correctly setting the starter stroke.

The member 32 may be threaded into the central piston 4 by means of athread 35, so that it is securely guided over a comparatively largedistance. The spring 33 effects on one hand, the avoiding of an overloadof the tension device and on the other hand, it permits the precisesetting of the tensional force by the spring 33. Since, at the end ofthe working stroke, the spring 33 is compressed, the tension force willnot substantially decrease, when at a pressure loss, the guide rollers14 abut an outwardly inclined area 30 of the collet 21 and force thecollet 21 together with the piston 3 until they are moved onto acylindrical or inwardly inclined area.

In the embodiments shown in FIGS. 4, and 5, a second roller 36 iscarried by the lever 11, with the roller 36 defining a sensor or feeler19. The rollers 36 are rolling off the inner wall 20 of cylinder 1,until they enter a circular space or area 37 which is somewhatdifferently shaped, but has in principle the same function as thecircular area 16 in FIGS. 1 and 2. The area 17 of flat conical shapemerges into the cylinder via a rounding 38. The rollers 14 move again inthe same manner as in FIGS. 1 and 2 at the end of the starting strokeonto the collet 21. The levers 11 are again urged outwardly and therollers 36 roll onto the area 17, whereby tension part 39 is moved by astrong force and a small distance in the direction 24.

In this embodiment, an insertable member 40, which in general is similarto the member 32 of FIGS. 1 and 2, is threaded together with the centralpiston 4 at 35 and is axially movably guided in the tension member 39.The supporting of the member 40 against the tension part 39 is, in thisembodiment, effected by means of cup springs 41 which have the samefunction as the springs 33 in FIGS. 1 and 2.

At the lower part of the central piston 4 is located a collar 42 similarto the collar 5 but the collar 42 is not mounted immediately adjacentthe central piston, but

is attached thereto by means of a bolt nut 43 via cup springs 44. A ring49 of an elastic material is inserted into bottom piece 50 of thecylinder 1 for the purpose of mounting the annular piston 3.

In this embodiment, the tension member is supported against the cylindernear the pivotal points of the levers 11. The supporting is constitutedby a circular collar or flange 48 by which the tension member 39 isguided in the cylinder.

In general, the function of the apparatus according to FIGS. 4 and 5 isthe same as that of FIGS. 1 and 2, and identical parts thereof areidentified by the same numerals.

The embodiment of FIG. 6 differs from FIGS. 4 and 5 and also from FIGS.1, 2 and 3 in that the collet 21 is provided with a uniform outwardlyinclined area 45 which changes into a cylindrical area 46. Furthermore,a tension part 47, which, in its function, is the same as the tensionpart 39 or 10, and which again is threaded together with the centralpiston 4, is connected immediately and without the insertion of aninsertable member 40 or 32 with the threaded connection member 34.

As shown by the drawings, the device of the present invention permitsthe performing of a working stroke after completion of a startingstroke, thereby enabling a very high application of power at a shorttensiondistance. If, for example, pressurized air with a pressure of 6over atmospheric pressure is available, it is then possible that astarting power of 200 kp may be utilized whereby a power ofapproximately 3,000 kp is obtained during the working stroke.

What is claimed is:

1. A work locating apparatus having a tension member actuated by meansof a piston movable within a cylinder, particularly a pneumaticcylinder, via a starting stroke and a working stroke, in which saidtension member is actuated with an amplified force by a mechanicalstep-up mechanism during the working stroke whereby said piston becomesreleasable from said tencollet having wedge-shaped outer surfaces whichcooperate with said guide portion of said swinging levers,

and said cylinder being provided with an abutment surface positionedtransversely to the axis of the cylinder with said abutment portions ofsaid swinging levers being pressed against said abutment surface duringthe working stroke.

2. The work locating apparatus as claimed in claim 1 in which the pistonis defined by an annular piston,

. a central piston encircled by the annular piston,

whereby said central piston is connected with the tension member, andsaid collet encircling the central piston.

3. The work locating apparatus as claimed in claim 2 in which thecentral piston is provided with a recess into which the guide portion ofthe lever, which lever is located at a distance from the rotation axis,may evasively move as long as that part of the lever defining theabutment portion contacts the inside wall of the cylinder, whereby thefront edge of the collet engages the guide portion during the startingstroke and the cylinder being provided with an enlarged area, which isdelimited axially at the side nearest to the annular piston I by meansof the abutment surface, and the abutment portion of the lever at thecompletion of the starting stroke enters the enlarged area, whereby theguide portion of the lever is moved to the wedge-shaped outer surface ofthe collet.

4. The work locating apparatus as claimed in claim 3 in which the frontedge of the collet engages a contact area of the guide portion, saidguide portion being tilted radially outwardly at the end of the startingstroke.

5. The work locating apparatus as claimed in claim 1, in which saidwedge-shaped outer surfaces of said collet constitute a conical surface.

'6. The work locating apparatus as claimed in claim 1, including apressure means which transmits the tension power and in which thepressure means is provided with a connector thread for receiving aselectively attachable connection member.

7. The work locating apparatus as claimed in claim 1 in which the partof the lever defining the abutment portion is formed according to asliding curve.

8. The work locating apparatus as claimed in claim 1 in which a pressuremeans which transmits the tension power, is supported against thetension member by means of interpolation of a spring means.

9. The work locating apparatus as claimed in claim 8 in which thepressure means is fixedly connected with the central piston.

10. The work locating apparatus as claimed in claim 8 in which thepressure means is carried in the tension member via a piston.

11. The work locating apparatus as claimed in claim 3 in which theabutment surface is arranged at a sloping angle to the stroke directionin the axial direction of the cylinder whereby said abutment surface isof a flat conical shape.

12. The work locating apparatus as claimed in claim 11 in which theabutment surface merges with a rounded intermediate section into theinside area of the cylinder.

13. The work locating apparatus as claimed in claim 1 in which the partof the lever defining the abutment portion is provided by a rollerpositioned in the lever.

14. The work locating apparatus as claimed in claim 3 in which thetension member is of cylindrical shape, and the enlarged area beinglocated in a first collar, said enlarged area being circular and beingprovided with a connecting means for a pressure supply.

15. The work locating apparatus as claimed in claim 3 in which theenlarged area of the cylinder is defined as a circular space and therecess of the central piston is defined as an annular tee-slot and aplurality of swinging levers being evenly distributed about thecircumference of the central piston and being positioned in the tensionmember.

16. The work locating apparatus as claimed in claim 15 in which thetension member is supported near the pivotal points of the leversagainst the cylinder, with the tension member being provided with athird collar which is circular, said tension member being guided in thecylinder by said third collar.

17. The work locating apparatus as claimed in claim 3, in which theguide portion is defined by a roller positioned in the lever.

18. The work locating apparatus as claimed in claim 2 in which thecentral piston is provided with a second collar which is placed on thecentral piston.

19. The work locating apparatus as claimedin claim 18 in which thesecond collar is spring biased towards the annular piston;

20. The work locating apparatus as claimed in claim 3 in which thetension member encircles the central piston to provide an annular recesswhich enables the insertion of the collet.

21. The work locating apparatus as claimed in claim 2 in which thecollet is provided with an outwardly inclined section merging with acylindrical section, the cylindrical section merging with a secondoutwardly inclined section and an inwardly inclined section merging withsaid second outwardly inclined section.

22. The work locating apparatus as claimed in claim 2 in which thebottom of the cylinder is provided with a ring of a plastic material,providing an elastic mounting for the annular piston.

1. A work locating apparatus having a tension member actuated by meansof a piston movable within a cylinder, particularly a pneumaticcylinder, via a starting stroke and a working stroke, in which saidtension member is actuated with an amplified force by a mechanicalstep-up mechanism during the working stroke whereby said piston becomesreleasable from said tension member and said piston actuates on the onehand, said tension member directly via said starting stroke and on theother hand, said step-up mechanism via said working stroke, theimprovement comprising swinging levers hinged on said tension member,each lever being provided with an abutment portion and a guide portion,said abutment portion being guided along the cylinder wall during thestarting stroke, a collet coaxial with said cylinder, said piston beingconnected to said collet, said collet having wedge-shaped outer surfaceswhich cooperate with said guide portion of said swinging levers, andsaid cylinder being provided with an abutment surface positionedtransversely to the axis of the cylinder with said abutment portions ofsaid swinging levers being pressed against said abutment surface duringthe working stroke.
 2. The work locating apparatus as claimed in claim 1in which the piston is defined by an annular piston, a central pistonencircled by the annular piston, whereby said central piston isconnected with the tension member, and said collet encircling thecentral piston.
 3. The work locating apparatus as claimed in claim 2 inwhich the central piston is provided with a recess into which the guideportion of the lever, which lever is located at a distance from therotation axis, may evasively move as long as that part of the leverdefining the abutment portion contacts the inside wall of the cylinder,whereby the front edge of the collet engages the guide portion duringthe starting stroke and the cylinder being provided with an enlargedarea, which is delimited axially at the side nearest to the annularpiston by means of the abutment surface, and the abutment portion of thelever at the completion of the starting stroke enters the enlarged area,whereby the guide portion of the lever is moved to the wedge-shapedouter surface of the collet.
 4. The work locating apparatus as claimedin claim 3 in which the front edge of the collet engages a contact areaof the guide portion, said guide portion being tilted radially outwardlyat the end of the starting stroke.
 5. The work locating apparatus asclaimed in claim 1, in which said wedge-shaped outer surfaces of saidcollet constitute a conical surface.
 6. The work locating apparatus asclaimed in claim 1, including a pressure means which transmits thetension power and in which the pressure mEans is provided with aconnector thread for receiving a selectively attachable connectionmember.
 7. The work locating apparatus as claimed in claim 1 in whichthe part of the lever defining the abutment portion is formed accordingto a sliding curve.
 8. The work locating apparatus as claimed in claim 1in which a pressure means which transmits the tension power, issupported against the tension member by means of interpolation of aspring means.
 9. The work locating apparatus as claimed in claim 8 inwhich the pressure means is fixedly connected with the central piston.10. The work locating apparatus as claimed in claim 8 in which thepressure means is carried in the tension member via a piston.
 11. Thework locating apparatus as claimed in claim 3 in which the abutmentsurface is arranged at a sloping angle to the stroke direction in theaxial direction of the cylinder whereby said abutment surface is of aflat conical shape.
 12. The work locating apparatus as claimed in claim11 in which the abutment surface merges with a rounded intermediatesection into the inside area of the cylinder.
 13. The work locatingapparatus as claimed in claim 1 in which the part of the lever definingthe abutment portion is provided by a roller positioned in the lever.14. The work locating apparatus as claimed in claim 3 in which thetension member is of cylindrical shape, and the enlarged area beinglocated in a first collar, said enlarged area being circular and beingprovided with a connecting means for a pressure supply.
 15. The worklocating apparatus as claimed in claim 3 in which the enlarged area ofthe cylinder is defined as a circular space and the recess of thecentral piston is defined as an annular tee-slot and a plurality ofswinging levers being evenly distributed about the circumference of thecentral piston and being positioned in the tension member.
 16. The worklocating apparatus as claimed in claim 15 in which the tension member issupported near the pivotal points of the levers against the cylinder,with the tension member being provided with a third collar which iscircular, said tension member being guided in the cylinder by said thirdcollar.
 17. The work locating apparatus as claimed in claim 3, in whichthe guide portion is defined by a roller positioned in the lever. 18.The work locating apparatus as claimed in claim 2 in which the centralpiston is provided with a second collar which is placed on the centralpiston.
 19. The work locating apparatus as claimed in claim 18 in whichthe second collar is spring biased towards the annular piston;
 20. Thework locating apparatus as claimed in claim 3 in which the tensionmember encircles the central piston to provide an annular recess whichenables the insertion of the collet.
 21. The work locating apparatus asclaimed in claim 2 in which the collet is provided with an outwardlyinclined section merging with a cylindrical section, the cylindricalsection merging with a second outwardly inclined section and an inwardlyinclined section merging with said second outwardly inclined section.22. The work locating apparatus as claimed in claim 2 in which thebottom of the cylinder is provided with a ring of a plastic material,providing an elastic mounting for the annular piston.